Republished from BrewingTechniques' March/April 1996.

High Terminal Gravities with Lager Fermentations

I have read that it is German brewery practice to let the yeast respire on the trub 8-12 hours before racking. Unfortunately, like most home brewers, I underpitch (the sediment from 1 qt of starter culture), so my beer normally takes 24-36 hours to develop a good head of krausen.

Should I pitch and aerate immediately after chilling and then rack off the trub just before low krausen (about 24 hours), increase the length or vigor of my aeration, culture a larger amount of yeast for pitching, or scavenge the sediment from the last batch and acid wash it for reuse?

A: It's terribly frustrating when you try to improve things and your results are worse instead of better. Maybe this is the reason why so many brewers are set in their ways. Once you have a system that works, you are reluctant to change anything. On the other hand, any brewer worth his mash is always going to be trying to find ways to improve the beer.

Before getting into the fermentation as such, let me comment on something you brought up: "fruitiness." Yeast strain plays a big role in ester production. Switching to another yeast strain may help as much as any changes you can make in your procedures. It sounds like you are definitely on the right track, and, in fact, your proposed remedies all might be of some benefit. The problem is, without more specific information about your procedure I am unable hazard a guess about which of these remedies might help the most. In particular, I would need more detail about your cold-trub separation method, more than simply that you rack the wort off the cold trub before you pitch and aerate. I believe it is best to pitch and aerate the cold wort immediately after cooling, as you suggest. The sooner the yeast starts to grow, the sooner it can crowd out any stray bacteria that may have been picked up during the cooling step. Rack the wort off the cold trub as soon as fermentation begins.

Your comment about underpitching is very significant. Trub removal does affect yeast growth somewhat, so if you try to make the best beer possible and decide to remove cold trub, you must also try to pitch an adequate quantity of healthy yeast. If your propagation procedures are good, 1 qt of starter should be sufficient for a 5-gallon batch, but be sure to pay attention to the following:

One issue I have not addressed is starter gravity, which is controversial. Some brewers think you get more yeast growth from a low-gravity wort (original gravity ~1.025); others think the starter wort should be close to the intended pitching wort to avoid surprising the yeast when they are pitched. Personally, I follow the low-gravity method, but both strategies work. At least I can testify that if you do everything else right, propagating yeast in a low-gravity wort will yield a very satisfactory fermentation.

Your question about repitching can be partially answered by referring to a question I answered in the previous issue of BrewingTechniques. Briefly, yes, repitching is a perfectly good practice, but it must be done properly. The yeast slurry for repitching must be fresh, taken from a batch that was brewed no more than two weeks ago (though you may be able to stretch that a bit with lagers), and it must have been stored cold (32-38°F [0-3°C]) under a layer of beer.

As for acid washing, this is something I do not recommend as a routine practice. It's like chemotherapy. It will kill contaminating bacteria, but it will also darn near kill the yeast cells. You might consider a water wash, which is not as effective at killing bacteria but will reduce their numbers considerably and help remove the trub that tends to accumulate on the yeast cells. The procedure is described briefly in my new book (2). Be sure to use dechlorinated water.

Thermal-Shocking Yeast

A: I was surprised by this question, because I have never paid any attention to the problem - if there is one - of shocking yeast by suddenly immersing them in a warmer environment. Like many microbrewers, I pull my yeast slurry from the bottom of the unitank no more than half an hour before knocking out. It goes into a sanitized bucket, which is dumped into the empty fermentor. There it sits, warming up a little, I suppose, during the brief time that it waits for the wort. The slurry is usually very cold when I pull it - typically 32-36°F (0-2°C). I have never had a long lag period with this procedure. As far as I can tell, thermal shock is not a problem when you go from colder to warmer.

To confirm my seat-of-the-pants impression, I checked with Dr. Joseph Power of the Siebel Institute of Technology (Chicago). To the best of his knowledge, the brewing literature contains no study of precisely the issue of slow versus fast warming of a yeast slurry. The one study he knows that concerns thermal shocking of yeast by rapid warming was done by researchers outside the brewing industry, and their target temperature was about 122°F (50°C). In that experiment, thermal shock did occur; however, Power's opinion - based on years of experience and a broad knowledge of general industry practice - is that thermal shock is not a problem when you pitch a 32°F (0°C) slurry into pitching-temperature wort.

The reason slurry is usually kept cold until right before pitching is that autolysis will set in once you warm the slurry past about 40°F (4°C). Autolysis can seriously degrade the viability of the yeast if it proceeds for any length of time. For this reason, the generally accepted wisdom is to keep the pitching slurry as cold as possible, down to 32°F (0°C), until immediately before use.

Though you did not ask about it, you may be interested to know that if you go the other way - rapid cooling - yeast can be shocked quite seriously, something to keep in mind when you propagate yeast at room temperature and pitch into cool wort. According to Power, the maximum rapid temperature drop that yeast can handle is about 18°F (10°C). This means that if you have a yeast starter at 68°F (20°C), for example, you should pitch it into wort no cooler than 50°F (10°C). Depending on your room's environment and your usual fermentation practices, you could easily exceed this limit when working with lager yeasts.

If you do work with lager yeast here's my recommendation: If your starter is more than 18°F (10°C) warmer than your intended fermentation temperature, I suggest pitching at a warmer temperature to avoid cold-shocking the yeast. Then ramp the temperature down over the next couple of days. Based on my experience, a ramp or 3-4°F per day works well. For example, if your starter is 75°F and you want to ferment at 50°F, cool the wort only to 57°F. Pitch the starter, and over the next 48 hours bring it down to 50°F. Note that with some yeast strains this method may yield more diacetyl in the finished beer. To minimize, try a diacetyl rest (explained in previous columns). If even that does not work, you may have to switch yeast strains or control the temperature of your starters.

Iron in the Water Supply

Although I have a hack test kit to measure the iron level, I don't know of any way to lower it, save installing a reverse-osmosis system, an alternative that is too expensive right now. Generally, I don't brew if the iron level is above 0.5 mg/L.

With these conditions, what should I expect from my yeast cultures? I have had trouble maintaining a viable culture for more than a few months, and my fermentations are never really active. Liquid yeasts have been especially difficult to work with. Even when I start with a 250-mL starter followed by a 1-L starter, I don't get much of a krausen head. (I usually aerate my wort using an aquarium pump with a 6-micron filter for 30-45 minutes.) I generally maintain fermentation temperatures at recommended levels (45-55°F [7-13°C] for lagers, 55-65°F [13-18°C] for ales). Attenuation is usually in the 65-75% range.

What is the upper limit for iron levels? How does iron affect the pathology of yeast, and what happens to the yeast when iron levels are at, say, 0.5 mg/L?

The water also contains 30-40 mg/L of magnesium, which should be good for the yeast but may adversely affect the flavor. (According to your book The Complete Handbook of Home Brewing [3], it may produce sour overtones. And yes, my beers do often have a sour note.)

Is there any hope of using this water, or must I resort to purchasing bottled water at $6 per bottle? I do boil my water before each session and usually remove 150-175 mg/L of what appears to be mainly chalk. Occasionally, I also get some rust in the sediment.

One final note: My water is hard, ~375-400 mg of calcium carbonate per liter of water.

A: I have never heard of the water treatment you mention for iron. A common treatment method is to aerate the water, which will cause the iron to oxidize and sediment in water-treatment plant settling tanks to be filtered out. In any case, if you can taste iron in the water, or if you can see rust in the kettle after boiling, the water contains too much. In fact, anything over 1 mg/L is reason enough to either treat or replace your water, if only for reasons of taste.

Carbon filters do not remove iron. You need either a reverse-osmosis filter or an ion-exchange filter. Rather than worry or wonder about whether iron is the culprit in my fermentation troubles, I would try brewing an experimental batch with distilled water. Use the distilled water for the yeast starters as well as the main batch. Don't forget that your mash's pH will probably be different and will have to be adjusted with calcium salts (carbonate to raise, sulfate or chloride to lower) to match the pH you get with boiled tap water. Follow an established recipe and change only the water. If your fermentation improves, then you know it's time to start saving up for a reverse-osmosis or ion-exchange filter (ion-exchange filters may be cheaper initially). If not, then you will have to consider other possible causes for your fermentation troubles. One observation I can make now is that your fermentation temperature range for ale is pretty low; most ales are fermented between 65 and 75°F (18-24°C).

High-Gravity Brewing

A: Sure, that will work. All big commercial breweries do something similar. They call it high-gravity brewing.

A couple of things to watch out for: If you dilute the wort with cold water before boiling or fermentation, make sure the water is dechlorinated (boiled or carbon filtered). If you add water after fermentation, make sure the water is dechlorinated and deaerated. Boiling is probably the simplest way to deaerate water and has the added benefit of killing microbes. Be sure to keep the kettle closed during cooling to prevent exposure to contaminants.

Weighing the Risks of Hot-Side Aeration

Should I risk the hot-side aeration that I may get from transferring (pouring) the mash from a mash tun to a lauter tun, or should I put up with difficult temperature maintenance?

A: Any time you move the mash around you will get some aeration, but if you do it carefully and gently, the amount of air you pick up in moving the mash from one kettle to another should be small. Most hot-side aeration takes place during the transfer of wort from the lauter tun into the kettle and to a lesser extent during the vorlauf (recirculation) before runoff begins. Moving hot wort from the kettle to another vessel (a hop back, for example) before cooling can also cause a lot of air to be picked up. When the trade-off is between a small amount of air pickup and a large risk of scorching, incomplete conversion, or other problems that can have a major effect on wort quality, the choice seems clear. If you want to do step mashing, do it in a separate mash kettle and transfer the mash to a separate, dedicated lauter tun for sparging. If you are content with a single-infusion mash and your only concern is the temperature drop during the mash stand, you can insulate the mash/lauter tun.

Alpha-Amylase, Beta-Amylase, and Sweet Fermentables

A: Yes, alpha-amylase does create fermentable sugars. Basically, the only product of beta-amylase action is maltose, which usually amounts to 45-55% percent of the soluble carbohydrates in beer wort. The remainder - glucose, maltotriose, and dextrins - are made by alpha-amylase alone. Glucose and maltotriose are both fermentable and both taste sweet.

I'm not sure just where the dividing line falls between sweet and tasteless sugars. I know that maltotriose is not as sweet as maltose, which in turn is not as sweet as glucose. I can't imagine that anything much longer than maltotriose would have much sweetness. But not all of a beer's sweetness comes from residual carbohydrates. Other compounds in beer (glycerol, for example, a by-product of fermentation) also taste sweet.

Sparge Temperature

A: The critical thing is the temperature of the mash, not the sparge water. You must keep the temperature down to avoid getting tannins and unconverted starch into the wort. The sparge water temperature is held down only because, as the sparge progresses, the mash temperature will slowly rise to the water temperature.

Some brewers begin sparging with very hot water - say 185°F (85°C) - to raise the mash temperature quickly. This is an alternative to the mash-out step if you do single-infusion mashes in a combination mash/lauter tun. Once the mash temperature has risen, however, you must lower the temperature of the sparge water to avoid overheating the mash.

References

(2) Dave Miller, Dave Miller's Homebrewing Guide (Storey Communications, Pownal, Vermont, 1995).

(3) Dave Miller, The Complete Handbook of Home Brewing (Storey Communications, Pownal, Vermont, 1988).